in this i have to improve the

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-4

of 4 votes

2
Answers
in this i have to improve the enqueue function
enqueue returns the queue after adding the element but the original queue is not to be changed
and same is for dequeue function

import java.util.ArrayList;
import java.util.List;
import java.util.NoSuchElementException;

public class PersistentQueue<E>{
private List<E> queue;

public PersistantQueue<E>(){
queue=new ArrayList<E>();
}

private PersistentQueue(List<E> queue){
this.queue=queue;
}

public PersistantQueue<E> enqueue(E e){
/*
Returns the queue that adds an item into tail of this queue without modifying this queue ( how to return without cloning ??)
*/
if(e==null){
throw new IllegalArgumentException();
}
List<E> clone = new ArrayList<E>(queue);
clone.add(e);
return new PersistantQueue<E>(clone);
}

public PersistantQueue<E> dequeue(){
/*
Returns the queue that removes the object at the head of this queue without modifying this queue ( here also how to do instead of clone as it it slow ??)
*/
if(queue.isEmpty()){
throw new NoSuchElementException();
}
List<E> clone = new ArrayList<E>(queue);
clone.remove(0);
return new PersistantQueue<E>(clone);
}

public E peek(){
if(queue.isEmpty()){
throw new NoSuchElementException();
}
return queue.get(0);
}

public int size(){
return queue.size();
}
}
- Sarvesh November 02, 2013 in United States | Report Duplicate | Flag | PURGE
Data Structures

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of 0 vote

Decorator Pattern

- Sunil Singhal November 03, 2013 | Flag Reply

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of 0 vote

First of all, it's obvious that the second new operation in enqueue() and dequeue() method is rebundant.
Then, as copy is so often to do, I suggest that your PersistentQueue implement Cloneable interface. Thus the way of creating a copy in enqueue() and dequeue() method could use clone() method, which is faster than new. This might be an improvement.

public class PersistentQueue<E> implements Cloneable{ 
    private List<E> queue;
    public PersistantQueue<E> clone(){
        PersistantQueue<E> copy = null;
        try{
            copy = (PersistantQueue<E>)super.clone();
            copy.queue = (list<E>)this.queue.clone();
        }
        catch(CloneNotSupportedException e){
            e.printStackTrace();
        }
        return copy;
    }
    public PersistantQueue<E> enqueue(E e){ 
        if(e == null){ 
            throw new IllegalArgumentException(); 
        } 
        List<E> copy = clone(); 
        copy.add(e); 
        return copy;
    } 
    public PersistantQueue<E> dequeue(){ 
        if(queue.isEmpty()){ 
            throw new NoSuchElementException(); 
        } 
        List<E> copy = clone(); 
        copy.remove(0);
        return copy;
    } 
}

- uuuouou November 30, 2013 | Flag Reply

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